Your fallacy of logic here is in the establishment of "moral" reasons that make it acceptable, and "immoral" reasons that cause it to be forbidden.
My argument is that the Founders articulated a principle as justification for their own Independence from England, and that justification was "consent of the governed."
The principle, which they articulated as a right based on Natural Law, is
"That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, — whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."
There are no "if they have the right morality" qualifiers in there. "Morality" is in the eye of the beholder.
In life there are good reasons to do things and bad reasons to do things. People and governments do things for good reasons and they do them for bad reasons.
We all know this to be a self evident reality.
Just because you are allowed to make a decision doesn’t mean you ought to, if you are doing it for an idiotic or immoral reason.
And with any decision there are consequences. No one stopped them seceding. But there were consequences. I personally believe if they had done it for good moral reasons they would have ultimately wound up winning and would have been a separate nation.